Active dry granular flows: rheology and rigidity transitions

The constitutive relations of a dense granular flow composed of self-propelling frictional hard particles are investigated by means of DEM numerical simulations. We show that the rheology, which relates the dynamical friction $\mu$ and the volume fraction $\phi$ to the inertial number $I$, depends on a dimensionless number $\mathcal{A}$, which compares the active force to the confining pressure. Two liquid/solid transitions -- in the Maxwell rigidity sense -- are observed. As soon as the activity is turned on, the packing becomes an `active solid' with a mean number of particle contacts larger than the isostatic value. The quasi-static values of $\mu$ and $\phi$ decrease with $\mathcal{A}$. At a finite value of the activity $\mathcal{A}_t$, corresponding to the isostatic condition, a second `active rigidity transition' is observed beyond which the quasi-static values of the friction vanishes and the rheology becomes Newtonian. For $\mathcal{A}>\mathcal{A}_t$, we provide evidence for a highly intermittent dynamics of this 'active fluid'.Comment: 7 pages, 7 figures, final version, accepted for publication in Europhys. Let

Estimation and Inference for Threshold Effects in Panel Data Stochastic Frontier Models

One of the most enduring problems in cross-section or panel data models is heterogeneity among individual observations. Different approaches have been proposed to deal with this issue, but threshold regression models offer intuitively appealing econometric methods to account for heterogeneity. We propose three different estimators that can accommodate multiple thresholds. The first two, allowing respectively for fixed and random effects, assume that the firms specific inefficiency scores are time-invariant while the third one allows for time-varying inefficiency scores. We rely on a likelihood ratio test with m − 1 regimes under the null against m regimes. Testing for threshold effects is problematic because of the presence of a nuisance parameter which is not identified under the null hypothesis. This is known as Davies problem. We apply procedures pioneered by Hansen (1999) to test for the presence of threshold effects and to obtain a confidence set for the threshold parameter. These procedures specifically account for Davies problem and are based on non-standard asymptotic theory. Finally, we perform an empirical application of the fixed effects model on a panel of Quebec dairy farms. The specifications involving a trend and the Cobb- Douglas and Translog functional forms support three thresholds or four regimes based on farm size. The efficiency scores vary between 0.95 and 1 in models with and without thresholds. Therefore, productivity differences across farm sizes are most likely due to technological heterogeneity.Stochastic frontier models, threshold regression, technical efficiency, bootstrap, dairy production, C12, C13, C23, C52, Research Methods/ Statistical Methods,

Overcoming the Energy Efficiency Gap: A Motivation, Opportunity and Ability Approach

Master'sMASTER OF ENGINEERIN

Utilisation de grilles de calcul pour la génomique comparative

International audienceLarge scale phylogenomics and comparative genomics require complex computational methods (parsimony, maximum likelihood, bayesian methods, MCMC, etc.) associated with massively distributed calculation. In this respect, grid computing plays a crucial role. Here we present how we processed exhaustive similarity searches on several millions of sequences with BLAST, using two different grids (TIDRA and GRISBI)

Investigating the influence of (Deoxy)fluorination on the lipophilicity of non-UV-active fluorinated alkanols and carbohydrates by a new log P determination method

Property tuning by fluorination is very effective for a number of purposes, and currently increasingly investigated for aliphatic compounds. An important application is lipophilicity (log?P) modulation. However, the determination of log?P is cumbersome for non-UV-active compounds. A new variation of the shake-flask log?P determination method is presented, enabling the measurement of log?P for fluorinated compounds with or without UV activity regardless of whether they are hydrophilic or lipophilic. No calibration curves or measurements of compound masses/aliquot volumes are required. With this method, the influence of fluorination on the lipophilicity of fluorinated aliphatic alcohols was determined, and the log?P values of fluorinated carbohydrates were measured. Interesting trends and changes, for example, for the dependence on relative stereochemistry, are reporte

Oriented Attachment of ZnO Nanocrystals

Self-organization of nanoparticles is a major issue to synthesize mesoscopic structures. Among the possible mechanisms leading to self-organization, the oriented attachment is efficient yet not completely understood. We investigate here the oriented attachment process of ZnO nanocrystals preformed in the gas phase. During the deposition in high vacuum, about 60% of the particles, which are uncapped, form larger crystals through oriented attachment. In the present conditions of deposition, no selective direction for the oriented attachment is noticed. To probe the driving force of the oriented attachment, and more specifically the possible influence of the dipolar interaction between particles, we have deposited the same nanocrystals in the presence of a constant electric field. The expected effect was to enhance the fraction of domains resulting from the oriented attachment due to the increased interaction of the particle dipoles with the electric field. The multiscale analytical and statistical analysis (TEM coupled to XRD) shows no significant influence of the electric field on the organization of the particles. We therefore conclude that the dipolar interaction between nanocrystals is not the prominent driving force in the process. Consequently, we argue, in accordance with recent theoretical and experimental investigations, that the surface reduction, possibly driven by Coulombic interaction, may be the major mechanism for the oriented attachment process

Chemsex Practices and Health-Related Quality of Life in Spanish Men with HIV Who Have Sex with Men

Chemsex, a new risky sexual behavior involving participation in sexual relations under the influence of drugs, has shown a significantly increased prevalence in recent years. This fact entails a serious public health issue, especially when Chemsex is practiced by individuals with an HIV (Human Immunodeficiency Virus) diagnosis. Hence, analyzing the characteristics of Chemsex practices, associated sexual practices and the health outcomes of individuals who participate in Chemsex, is extremely important. The main aim of the present study is to analyze the prevalence and characteristics of the practice of Chemsex in a sample of 101 men with HIV who have sex with men who attended the Department of Infectious Diseases of the General University Hospital of Alicante (Spain). Furthermore, the association between Chemsex and Health-Related Quality of Life (HRQoL) was also assessed. Chemsex and sexual practices were evaluated by employing a questionnaire applied on an ad hoc basis. HRQoL was assessed by employing the Medical Outcomes Study HIV Health Survey (MOS-HIV). In total, 40.6% of the participants had practiced Chemsex during the last year. When sexual practices were compared between those individuals who practiced Chemsex and those who did not, the former presented a higher level of risky sexual behaviors, especially with occasional and multiple sexual partners. Regarding HRQoL, those individuals who practiced Chemsex exhibited a poorer HRQoL in the majority of domains, especially those participants who practiced it with a higher intensity. The present study points out the high prevalence of Chemsex practice between men with HIV who have sex with men in Spain. Moreover, this study highlights the negative effects of Chemsex on HRQoL, probably due to the mixed effects of higher levels of risky sexual practices and the consequences of drug consumption.This research was funded by the Office of the Vice President of Research and Knowledge Transfer of the University of Alicante, Grant Number: GRE-18-17B

Impact of COVID-19 Pandemic on Academic Stress and Perceived Classroom Climate in Spanish University Students

The COVID-19 pandemic has caused several changes in society, especially in the educational context, where several learning methodologies and social interactions have been modified significantly. This fact could have had a negative impact on academic stress levels of students and the classroom climate, especially in the university context. The main aim of the present study was to identify changes in academic stress and the perceived classroom climate caused by COVID-19 in a sample of Spanish university students. Academic stress was evaluated trough the Stressor Academic Scale (SAS) and perceived classroom climate employing the Perceived Classroom Responsibility Climate (PCRC) questionnaire. A longitudinal study was conducted. 135 students (97 females and 38 males) from the Gastronomy (n = 31) and Criminology (n = 104) degrees were evaluated before and after the COVID-19 lockdown in Spain. Academic stress levels and perceived classroom climate were analyzed before (Time 1) and after (Time 2) the lockdown declaration. An increase in academic stress was found, especially in the categories regarding Teachers’ Methodological Deficiencies, Academic Over-Burden and Beliefs About Performances. Females and final year students suffered higher levels of academic stress. No differences were found between Time 1 and 2 in perceived classroom climate. The obtained results point out a significant increase of academic stress in university students due to the COVID-19 pandemic in Spain. The implemented educational changes and the uncertainty that resulted from the pandemic could have a significant negative impact on mental health in this population, resulting in higher levels of academic stress, especially in females and final year students. Future studies should analyze the strategies that students are employing to cope with these educational challenges and intervention strategies to promote them in the context of higher education.This research was supported by the Program of Networks-I3CE of Investigation in University Teaching (Program Networks) from the Vice-Rectorate of Quality and Educational Innovation and Education Sciences Institute of the University of Alicante (2019–2020). Ref.: (4913)

Pan-Tropical Analysis of Climate Effects on Seasonal Tree Growth

Climate models predict a range of changes in tropical forest regions, including increased average temperatures, decreased total precipitation, reduced soil moisture and alterations in seasonal climate variations. These changes are directly related to the increase in anthropogenic greenhouse gas concentrations, primarily CO2. Assessing seasonal forest growth responses to climate is of utmost importance because woody tissues, produced by photosynthesis from atmospheric CO2, water and light, constitute the main component of carbon sequestration in the forest ecosystem. In this paper, we combine intra-annual tree growth measurements from published tree growth data and the corresponding monthly climate data for 25 pan-tropical forest sites. This meta-analysis is designed to find the shared climate drivers of tree growth and their relative importance across pan-tropical forests in order to improve carbon uptake models in a global change context. Tree growth reveals significant intra-annual seasonality at seasonally dry sites or in wet tropical forests. Of the overall variation in tree growth, 28.7% was explained by the site effect, i.e. the tree growth average per site. The best predictive model included four climate variables: precipitation, solar radiation (estimated with extrasolar radiation reaching the atmosphere), temperature amplitude and relative soil water content. This model explained more than 50% of the tree growth variations across tropical forests. Precipitation and solar radiation are the main seasonal drivers of tree growth, causing 19.8% and 16.3% of the tree growth variations. Both have a significant positive association with tree growth. These findings suggest that forest productivity due to tropical tree growth will be reduced in the future if climate extremes, such as droughts, become more frequent